Hobson tightening torque chart
Stainless Steel Bolt Torque Chart: Class 50, 70 and 80, M3 to M39
Hobson's one-page technical chart of recommended tightening torques for stainless steel hex bolts. It lists pitch, stress area and torque in Nm for class 50, 70 and 80, from M3 to M39.
What this covers
- Pitch and stress area
- Torque by class 50, 70, 80
- Lubrication and k factor
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- Covers M3 to M39 in stainless property classes 50, 70 and 80.
- Recommended torque, M10: 15.8Nm class 50, 33.9Nm class 70, 45.2Nm class 80. M12: 27.6, 59.2 and 78.9Nm. M20: 133.8, 286.7 and 382.2Nm.
- The figures use a k factor of 0.2, which assumes burr-free threads and a good quality molybdenum disulphide (MoS2) lubricant. The figures are a guide only, based on the first tightening of a single assembly in isolation.
- Stainless fasteners that are not lubricated or coated often seize, and can have k factors above 0.35, so the chart figures assume lubrication.
Who it helps: Anyone tightening stainless bolts who needs a starting torque and wants to avoid galling.
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This document is published by Hobson Engineering, who supply this range to us. We show it here in full so you can read it next to the product; the summary above is ours. Read it on this page or download the PDF. For the most current version, ask us.